This invention relates to sensing systems.
The invention is more particularly concerned with sensing systems for use in measuring temperature and pressure.
It is common practice, in the electronic control of jet engines, to measure particular engine parameters, i.e. shaft speed, gas temperature and gas pressure, to determine engine conditions for control of fuel flow in response to a demand for power. Where particular parameters are necessary but are not readily available for the mathematical gas model, these can be obtained from others by inference.
The measurement of gas pressure and temperature are carried out by different sensors, such as, for example a pitot probe and a thermocouple junction respectively. Because of the gas flow conditions in jet engines, the pressure and temperature at closely spaced points can be very different. The usefulness of the pressure and temperature readings is, therefore, reduced because they relate to values at different locations in the gas flow. Using two sensors can also have the disadvantage that, if they are closely spaced, in an attempt to provide readings in respect of the same location, one sensor can alter the value sensed by the other sensor. For example, the pressure sensor may act as a heat sink and affect the temperature detected by the temperature sensor; the temperature sensor may interfere with gas flow over the pressure sensor and thereby affect the pressure reading Using two separate sensors and their associated cabling also leads to an increase in the total size and weight. In aircraft applications it can be advantageous to make as few as possible openings through the engine casing or aircraft skin; the need to mount two separate sensors can therefore be an additional disadvantage for this reason.